Real Dictionary

goldfish
countable noun: Goldfish are small gold or orange fish which are often kept as pets.

goldfish in American English
a small, golden-yellow or orange, freshwater cyprinoid fish (Carassius auratus) often kept in ponds and aquariums and represented by numerous domestic varieties
noun: a small, usually yellow or orange fish, Carassius auratus, of the carp family, native to China, bred in many varieties and often kept in fishbowls and pools

goldfish in British English
noun: a freshwater cyprinid fish, Carassius auratus, of E Europe and Asia, esp China, widely introduced as a pond or aquarium fish. It resembles the carp and has a typically golden or orange-red coloration